Radiation screen



Jan. 11, 1966 J. H. JARVIS, JR

RADIATION SCREEN 2 Sheets-Sheet 1 Filed Dec. 30, 1963 Jan. 11, 1966 Filed Dec. 50, 1963 J. H. JARVIS, JR

RADIATION SCREEN 2 Sheets-Sheet 2 United States Patent 3,228,362 RADIATHGN SCP EN James H. Jarvis, .ln, Weatogue, Conn, assignor to Combustion Engineering, Inc, Windsor, Conn, a corporation of Delaware Filed Dec. 39, 1963, Ser. No. 334,265 4 Claims. (Cl. 11(l-165) This invention relates to a heat shield and more particularly to a heat and splash shield for a sealed ash receptacle for a vapor generator furnace.

An object of this invention is an improved durable shield.

A further object is a shield which will absorb sudden local rapid temperature changes without serious deterioration.

Other objects and advantages will be apparent from the following specification and the attached drawings in which:

FIG. 1 is an end view, partly in section, of the shield formin the invention mounted on the ash hopper structure of a furnace and extending into an ash receptacle;

FIG. 2 is an enlarged end view of the shield and its support;

FIG. 3 is a side View of the shield showing a plurality of expansion joints;

FIG. 4 is a section through an expansion joint; and

FIG. 5 is a section through a corner expansion joint.

In a water tube boiler or vapor generator the combustion space in which fuel is burned may be defined by parallel, vertically extending water filled tubes forming what is known as furnace Walls and forming the side walls of the furnace. At the lower end of the combustion space the tubes indicated as 1!) in FIG. 1 are inwardly inclined towards each other from the opposite sides of the furnace as at 12 to form a trough 14 extending across the bottom of the furnace or combustion space and terminating in a discharge or opening 16 where the tubes are bent outwardly as at 18 and lead into headers 29. Each tube is Welded to the adjacent tube or other means provided to provide an air tight casing for the combustion chamber and the hopper 14.

Arranged beneath the opening 16 of the hopper 1 is an ash receptacle 22 having an open top 24 for receiving ash, slag, or scale discharge from the combustion chamber through the hopper 14. The ash receptacle 22 may be of any suitable materials such as concrete lined with refractory material and is provided with an opening 24 at the bottom thereof for discharge of material collected in the receptacle. The opening 24 may be closed by any suitable means, not shown, for retaining Water 25 in the receptacle and may be removed to permit washing of the material out of the receptacle.

The water 26 in the receptacle serves the purpose of protecting the receptacle from radiation and cooling the ash that is discharged through the discharge 16 and the hopper 14. The water also serves the purpose of cooling and breaking up slag and scale that may drop into the hopper 14 and through the opening 16. This slag and scale may come down in large chunks and sometimes from great heights such as one hundred feet or more and passing through the opening 16 will cause the water to splash.

Arranged around the outside of the receptacle 22 is a container 28 containing water 30 into which a shield 32 extends from the boiler tubes 18. The combustion space in the furnace and the hopper 14 may be under pressure such as say 16 inches of water during operation of the furnace and as the hopper opens directly into the receptacle 22 it is necessary to seal the receptacle in order to avoid loss of this pressure. The sealing plates ice 32 which are welded in air-tight relation to the tubes 18 dipping into the water 31) in the containers 28 which are arranged in air tight relation around the exterior of the receptacle 22 provide such a seal.

The opening or discharge orifice 16 of the hopper 14 exposes structure below the opening 16 to radiation from the combustion chamber. In order to protect this structure a shield 34 is suspended from the tubes 18 and surrounds the orifice 16. The shield 34 is arranged around the interior of the receptacle 22 and adjacent the walls thereof. Due to the range of temperature variation from cold to operating temperature, which may be 700 or more, and because the vapor generators are usually suspended on a framework from overhead, the bottom of the generator including the hopper l4 and the tubes 18 may move downwardly as much as ten inches from the cold to the hot condition. The shield 34 is therefore suspended from the tubes 18 so that it may slide freely into the open end 24 of the receptacle 22 as the vapor generator expands. Similarly the shields 32 may move freely downward in the container or trough 28 during this expansion.

The shields 34 may become quite hot, and may even become red hot, from the radiation through the opening 16 and particularly at the ends of the hopper trough 14. Slag falling through the hopper 14 and splashing into the water 26 will splash water onto the red hot shield. This alternate intermittent and repeated heating and sudden cooling is a very severe service and tends to rapid deterioration of the shield 34. Previous shields formed of Meehanite castings lined with refractory material have warped and deteriorated and Incoloy plates also failed after short periods of service. Steam generators once started may not be again shut down for long periods of time such as six months or longer and as it is necessary to shut the furnace down in order to replace the shields or drip plates 34 it is desirable to have shields that will last at least as long as the time between shut downs.

These shields serve the dual purpose of acting as a radiation shield to prevent the refractory material of the ash receptacle 22 and also the material of the seal plates 32 from becoming unduly heated and also serve the purpose of a splash shield for preventing any surfaces of the receptacle 22 or the seal plates 32 that may be heated from being splashed with water thrown about by slag dropping into the water pool 26. These shields 34 also act as dust shields preventing an undue amount of ash dust being carried over into the container 28 and settling in the water 30 from where it has to be eventually removed.

All of these desirable features can be accomplished with the screen of applicants invention which comprises a wire screen of suitable material such as stainless steel type 430 of say inch rods woven or welded to form a wire screen or cloth with say A to /2 inch openings. The Wire screen 36 which may be cut into suitable lengths to provide adequate expansion joints is folded upon itself at 38 so as to provide a trough 40. The upper ends 42 of the screen 36 at the upper end of the trough are brought close together on opposite sides of a plate or tabs 44 welded to the longitudinally extending portions 18 of the boiler tubes and are secured to the plate 44. This provides a double layer of the wire screen 36 which hangs free in the receptacle 22 and will serve as an adequate heat shield for both the receptacle 22 and the sealing plates 32. This permeable screen because of its double thickness and the comparatively small mesh openings will also act as an adequate dust shield for the water trough 28. This pervious wire screen or cloth because of its flexible nature and the open mesh construction will absorb localized stresses caused by the water splashing onto the hot screen and at the same time maintain the temperature of the refractory wall of the receptacle 22 and the seal plates 32 at a low temperature level such that if they were splashed by water no severe damage would result.

Due to the temperature range through which the screen 34 is heated and due to the difierence in that temperature range from the range through which the tubes 18 supporting the shield 34 is subjected it is necessary to provide expansion joints in the shield 34. As shown in FIG. 3, several joints may be provided lengthwise of the shield as it extends along the hopper 14. These joints may be formed by inserting a fiat piece of the Wire screening 48 between the folded up sides 36 of the trough 40 and allowing this piece 48 to extend into the trough of two adjacent shields. This filler piece 48 may be secured to the trough of one section of the shield by a bolt 50 and allowed to slide in the trough of the adjacent shield to provide for expansion.

The shield is generally rectangular in shape as it surrounds the discharge of the elongated hopper 14 and provision is made for an expansion joint at the corners of the shield by ending the individual sections of the shield short of the corners and then forming the corner of the shield by bending a separate piece or filler strip 52 to form the corner and inserting the opposite legs of the angularly bent piece 52 into the troughs of the respective adjacent shield lengths at the corner. One leg of the member 52 may be secured in one shield by the bolt 54 and allowed to slide in the trough of the adjacent shield so that expansion may be taken up by the sliding movement and distortion of the corner filler piece 52.

It is to be understood that the invention is not limited to the specific embodiment herein illustrated and de scribed but may be used in other ways without departure from its spirit and that various changes can be made which would come within the scope of the invention which is limited only by the appended claims.

I claim:

1. In combination, walls forming a water-containing ash receptacle, an ash hopper having a discharge opening discharging into said receptacle, an open mesh wire screen with openings hanging from said hopper structure adjacent the walls of said receptacle and extending into said receptacle an appreciable distance along said walls, pressure sealing means outside of said receptacle for sealing said receptacle and hopper, said screen located between said sealing means and said hopper discharge.

2. A shield as claimed in claim 1 comprising a wire screen folded on itself to provide a trough having a closed side and an open side, means connecting said open side to said hopper structure.

3. A shield as claimed in claim 2 in which the shield is made up of several lengths of wire screen joined together by expansion joints, said joints comprising a layer of wire cloth located in said trough and fastened to one length and free to move in an adjacent length.

4. A shield as claimed in claim 3 in which adjacent lengths of said shield are arranged at an angle and joined to each other by an expansion joint to form a corner, said corner comprising a layer of wire screen bent to form an angle with two legs, one leg located, and fastened, in the trough of one length and the other leg located in and free to move in the adjacent length.

References Cited by the Examiner UNITED STATES PATENTS 2,337,634 12/1943 Berry l10l65 2,275,652 3/1942 Pursel 1l0165 3,094,953 6/1963 Alexander 1l0l71 FREDERICK L. MATTESON, IR., Primary Examiner.

KENNETH W. SPRAGUE, JAMES W. WESTHAVER,

Examiners. 

1. IN COMBINATION, WALLS FORMING A WATER-CONTAINING ASH RECPTACLE, AN ASH HOPPER HAVING A DISCHARGE OPENING DISCHARGING INTO SAID RECEPTACLE, AN OPEN MESH WIRE SCREEN WITH OPENINGS HANGING FROM SAID HOPPER STRUCTURE ADJACENT THE WALLS OF SAID RECEPTACLE AND EXTENDING INTO SAID RECEPTACLE AN APPRECIABLE DISTANCE ALONG SAID WALLS, PRESSURE SEALING MEANS OUTSIDE OF SAID RECEPTACLE FOR SEALING SAID RECEPTACLE AND HOPPER, SAID SCREEN LOCATED BETWEEN SAID SEALING MEANS AND SAID HOPPER DISCHARGE. 